[Just so I get this right, since reading the MTG wiki has left me feeling rather nauseous...]
[The phyrexians that ztg is blowing up are cybernetically addled humanoids, that are themselves genetically engineered. They have a philosophy of attaining pure artificiality, and systematic destruction of that which is imperfect. Their biosphere, if you can call it that, is contaminated with an oil that has properties similr to grey goo. They are not very nice.]
[Their philosophy is mutually self refferential and also self conflicting. As a logican, I can clearly see outstanding faults in their logic. Likely, these faults, which they cling to axiomatically, will systematically prevent them from achieving their stated goals in their philosophy. The purely synthetic components of their beings must be more orderly and programmable. A rival strain of grey goo would be unspeakably destructive to them, as the corruption would be systemic, and every member of their "race" would see the infected as imperfect, and contaminated by the influence of an imperfect artifiier. It would initiate thermonuclear civil war, until all resources at their disposal would be eliminated by the conflict. At that point, it doesn't matter which contageon wins. There wouldn't be enough raw material for either side to rise up from the ashes, and they would no longer exist.]
[A rival grey goo could potentially be created by sending malicious software into a well contained sample of the genuine article, altering its behavior. Such a rival version could already exist on mirrodin, if independent cyber evolution has occured there, under different circumstances. Cross contaminating both artificial spheres should start the apocoplypse on both worlds.]
[This would be because both sets of artifice beings would believe themselves the exualted true creation, and hold it in perfect axiomatic regard. They would be unable to resolve the paradox: that they are the same, yet different. The mirrodin strain would be evolving with absolutely no guidance from their creator, and would have reached different conclusions on many deep hardware levels. "Real" phyrexians from their home plane would hold them in the highest possible disdain.]